1. Field of the Invention
The present invention relates to a power train, especially for a motor vehicle. More particularly, the present invention relates to a power train that includes an internal-combustion engine, a power output element, such as a transmission, positioned downstream of the engine in a power transmission path, and an energy conversion machine arranged in the power transmission path between the engine and the power output element, whereby the engine can be uncoupled from the power output element and/or from the energy conversion machine by at least one clutch.
2. Description of the Related Art
A power train of a type known in the art includes an engine, a transmission, and preferably an electrical machine or a flywheel, which is commonly designated an inertial energy device and which as a rule can be uncoupled by one clutch from the engine and by another clutch from the transmission. For example, when in the decelerating mode, such a design allows uncoupling the engine and, where called for, to shut it off, whereby with the clutch between the transmission and the inertial energy device engaged, the latter will acquire energy from the drive wheels through the transmission and, if appropriate, can supply the energy to an energy accumulator. Thus the inertial energy device acts as an energy conversion machine that converts the kinetic energy into electrical energy when applied to an electrical machine, or into rotational energy when applied to a flywheel. The energy so stored is available when restarting the engine, or it can be utilized for additional power when the vehicle is accelerating.
Such an energy-saving operation of the power train with a stopped engine involves a significant drawback. While the engine is shut off, accessories, which typically are mounted on the end of the drive shaft away from the transmission, will not be driven, that is, such accessories will not operate during the engine""s inactivity. That condition amounts to a shortcoming with respect to safety-related accessories such as power steering pumps, vacuum pumps for power braking, and also adversely affects comfort-enhancing accessories, such as air-conditioning compressors.
Accordingly, accessories already have been proposed that can be driven while uncoupled from the crankshaft, for example by being powered electrically. Such accessories however are expensive and also incur a significantly higher energy drain.
Moreover, the space available to integrate energy converters is frequently very limited, in particular in the case of transversely-mounted front engines.
Accordingly, it is an object of the present invention to provide a power train allowing energy-saving operation of at least the safety-related accessories, or those relating to comfort, the power train of the invention allowing economical and energy-saving manufacture and operation. Moreover, it is another object of the invention to reduce the axial space required by the power train.
This problem is solved by providing a power train, in particular one for vehicles, which includes at least an engine, a power output system configured in the power transmission path downstream of the engine, such as a transmission, and an energy converter arranged in the power transmission path between the engine and the power output system. The engine is detachably coupled by at least one clutch to the power output system and/or the energy converter and at least one accessory is drivingly connected to the energy converter, or it constitutes the converter.
Such a power train advantageously is fitted with a first and a second clutch, one of which separates the energy converter from the engine and the other of which separates the energy converter from the power output system. The accessory at least relates to safety or enhances comfort, such as a pump, a compressor, or the like. For example, an accessory can include a power steering pump, a power brake booster, or a vacuum pump to service a power brake booster, or a compressor, for example an air-conditioning compressor. It should be understood that additional accessories also can advantageously be included in the design of the invention. Moreover, an additional or several additional accessories can advantageously be made to operate in association with the energy converter.
Preferably, the energy converter is arranged coaxially about the axis of the drive shaft of the power train. Thus, it can be mounted coaxially with the crankshaft or coaxially with the transmission input shaft. It also can be advantageous to mount the energy converter approximately axially parallel to the drive shaft axis and to provide the power transmission path between the drive shaft axis and the energy converter in the form of a belt drive, a continuously variable drive, a gear drive, or the like, for example using a chain drive or a gear drive. In a further advantageous manner, the at least one accessory can be arranged axially parallel to the drive shaft axis, or it can be arranged in a unitary structure that includes the accessory and the energy converter. Within the conception of the present invention, furthermore, and similar to a belt drive, several units, for example the energy converter and at least one accessory, can be drivingly connected by a belt drive at the front side of the transmission.
If when decelerating the engine is standing idle, the clutch between it and the inertial energy storage system, functioning as an energy converter, can be disengaged. And if the clutch between the energy converter and the transmission is engaged, or if there is no clutch connected with the transmission, the kinetic energy of the vehicle can be transferred to the energy converter. In that manner the energy converter can supply energy directly to at least one accessory by way of the transfer of converted energy, or the accessory can be directly driven by the energy converter, the energy from which is conveyed at the same time that the vehicle is slowing down.
In this respect it can be advantageous, depending on the desired vehicle motion, either by retarding movement through the storage of energy in the energy converter, or by a desired acceleration of movement when the engine is standing idle, or, for example, to start the engine by means of the energy converter, to engage or disengage in a known manner the at least one clutch between the engine and the energy converter, or, if there is a second clutch between the energy converter and the transmission, to engage or disengage the second clutch. In addition to supplying at least one accessory, it can be advantageous to use the energy converter to change kinetic energy into another form of energy. This latter form of energy can be energy of rotation, for example when the energy converter includes a flywheel, or electrical energy if the energy converter is an electrical machine, or it can be thermodynamic energy if the energy converter is a compressor, for example for compressing a critical gas, or a vacuum pump, or the like. It should be understood that the energy converter can convey such input energy to an appropriately designed storage device for disposition, or an accessory, for example an air-conditioning compressor, also can receive and store energy and, if called for, can feed that energy into the overall power train.
An advantageous embodiment of this invention concerns a power train with a continuously variable transmission (CVT) the transmission ratio of which is adjusted by sets of disks that are movable by an hydraulic pump, as disclosed in German Patent Publication DE 199 23 851. Such hydraulic pumps are frequently driven by the transmission input shaft. If there is at least one clutch provided between the energy converter and the engine, then if the clutch is in a disengaged condition, for example during recuperation or when the motor vehicle is being driven, then the hydraulic pump can be driven by the energy converter. The operational connection between the hydraulic pump, acting as an accessory in the sense of the present application, and the energy converter can be a belt drive or a chain drive, preferably also having a variably adjustable transmission ratio, or a gear drive, a friction wheel drive, or split power gearing. In an especially advantageous manner, that embodiment can include an additional clutch between the CVT and the energy converter, as a result of which the energy converter can, substantially independently of the rotational speeds of the transmission input shaft and of the crankshaft, drive the hydraulic pump in the disengaged or in the slipping condition of the clutches, and thereby advantageous operation of those elements can be attained, especially with a variably adjustable transmission ratio between the hydraulic pump and the energy converter. In one aspect, for example, the energy-converter""s flywheel mass can be accelerated during braking of the motor vehicle, and the hydraulic pump can be operated by rotational energy while the vehicle is stopped. Of course, during this phase additional electrical energy can be gained from the rotational energy, or electrical energy can be converted into rotational energy, especially if a substantially long vehicle stop is anticipated. A resulting advantage, for example, is that when starting and at low engine rotational speeds enough pressure is available to adjust the sets of disks, and thereby the transmission ratio, by means of the pressure made available by the hydraulic pump, and as a consequence the engine can transfer more driving power during the starting process